All pleurotos kinds which are cultivated have tough stems which account for approximately 20 to 25% of the production and which are thrown away as waste. The fruit body spoils easily. They get tougher through storage in a refrigerator. Freezing is only suitable after previous blanching. Dried mushrooms become like rubber after dehydration (TR. Gormely and F. O'Riordian, Lebensm.-Wiss. u. Techn., Bd.9 (1976) S 75-78). All other applied means of conservation require a more or less extensive heat treatment, but each heat treatment (blanching, cooking, sterilization, drying) increases the toughness of the fruit body and especially that of the stems.
Fermentation of the mushrooms was repeatedly tried in the past. Apart from the long duration, the adding of sugar and the lack of controlling the fermentation, this method was disadvantageous because the material had to be blanched. (W. Botticher, Technology der Pilzverwertung, Verlag Eugen Ulmer, 1974). Quick silaging (R. Kselig, Ceska, mykol, 10, 1956, p. 190) required previous boiling of the mushrooms for 10 to 15 minutes. Without sterilization the product lasted for only 2 to 3 days. Therefore, the previously used methods of conservation are not suitable.